Hermiston, Oregon climate: Normal weather by month, frost dates and records
Hermiston's normal year runs from 28°F December nights to 93°F July afternoons, with 8.6 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 12.2°C, December lows of −2°C, July highs of 34°C, 219 mm of precipitation a year.
- NOAA stationHermiston Municipal Airport
- Station IDUSW00004113
- Location45.83°N 119.26°W
- Elevation641 ft (195 m)
- From the center1 miles
- Population19,746
On October 23, the normal high in Hermiston is 63°F and the normal low 37°F, and the chance of measurable rain or snow is 27%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Hermiston.
- Jan 43° 29°
- Feb 49° 29°
- Mar 59° 34°
- Apr 67° 39°
- May 76° 46°
- Jun 82° 53°
- Jul 93° 59°
- Aug 91° 57°
- Sep 81° 48°
- Oct 67° 39°
- Nov 51° 32°
- Dec 42° 28°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Hermiston each month?
July is the warmest month, with normal highs of 93°F; December the coldest, with normal lows of 28°F. The most precipitation falls in January (1.14 in), the least in July (0.12 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 43°F | 29°F | 36.0°F | 1.14 | 10 | <1 | 21 | 9 h |
| February | 49°F | 29°F | 39.3°F | 0.86 | 8 | <1 | 20 | 10 h 20 min |
| March | 59°F | 34°F | 46.4°F | 0.77 | 8 | <1 | 16 | 11 h 50 min |
| April | 67°F | 39°F | 52.8°F | 0.78 | 7 | <1 | 7 | 13 h 30 min |
| May | 76°F | 46°F | 61.2°F | 0.83 | 8 | 2 | 1 | 14 h 50 min |
| June | 82°F | 53°F | 67.6°F | 0.64 | 5 | 6 | <1 | 15 h 40 min |
| July | 93°F | 59°F | 75.6°F | 0.12 | 2 | 20 | <1 | 15 h 20 min |
| August | 91°F | 57°F | 73.9°F | 0.17 | 2 | 18 | <1 | 14 h 10 min |
| September | 81°F | 48°F | 64.6°F | 0.33 | 3 | 4 | <1 | 12 h 40 min |
| October | 67°F | 39°F | 52.7°F | 0.80 | 8 | <1 | 9 | 11 h |
| November | 51°F | 32°F | 41.5°F | 1.05 | 10 | <1 | 17 | 9 h 30 min |
| December | 42°F | 28°F | 35.2°F | 1.12 | 11 | <1 | 23 | 8 h 40 min |
| Year (annual) | 67°F | 41°F | 53.9°F | 8.61 | 80 | 50 | 115 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 6°C | −2°C | 2.2°C | 29 mm |
| February | 10°C | −2°C | 4.1°C | 22 mm |
| March | 15°C | 1°C | 8.0°C | 20 mm |
| April | 19°C | 4°C | 11.6°C | 20 mm |
| May | 25°C | 8°C | 16.2°C | 21 mm |
| June | 28°C | 12°C | 19.8°C | 16 mm |
| July | 34°C | 15°C | 24.2°C | 3 mm |
| August | 33°C | 14°C | 23.3°C | 4 mm |
| September | 27°C | 9°C | 18.1°C | 8 mm |
| October | 19°C | 4°C | 11.5°C | 20 mm |
| November | 10°C | 0°C | 5.3°C | 27 mm |
| December | 6°C | −2°C | 1.8°C | 28 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Boardman (21 miles away), gets 4 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00004113; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Hermiston?
Normal highs sit between 65°F and 85°F in April, May, June, September and October. Of those, September has the fewest days with rain (3).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00004113.
When is the last frost in Hermiston?
In Hermiston, the last spring frost (32°F) comes after April 26 in half of years and after May 10 in one year in ten; the first autumn frost comes before October 10 in half of years and before September 25 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 261 year in 10 after May 10; 9 in 10 after April 9
- First autumn frost, half of years before
- October 101 year in 10 before September 25; 9 in 10 before October 26
NOAA puts the median frost-free season at 167 days, and the season without a hard freeze (28°F) at 196 days.
A hard freeze (28°F) comes after April 9 in half of springs and before October 24 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Hermiston in zone 7b in ZIP code 97838, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Hermiston's NOAA station is in zone 7a: the coldest night of a typical year reaches 2°F (22 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Oregon · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00004113; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Hermiston?
In a normal year in Hermiston, 50 days a year reach 90°F (10 of them 100°F or more), 115 nights fall to 32°F or colder and 80 days bring measurable precipitation.
- Days at 90°F or more
- 50a normal year
- Days at 100°F or more
- 10a normal year
- Nights at 32°F or colder
- 115a normal year
- Days that stay below freezing
- 14high of 32°F or less
- Days with 0.01 inch of precipitation
- 80a normal year
The highest temperature in this station's record (since 1998) is 118°F, on June 29, 2021; the lowest is −16°F, on December 16, 2008.
The wettest calendar year on that record is 2012, with 12.93 in.
Source: NOAA NCEI 1991-2020 annual normals, station USW00004113; records: ACIS (NOAA Regional Climate Centers), station USW00004113. Records use complete months only; a month missing more than three days is left out.
How sunny is Hermiston?
Over a year 78% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Hermiston, 4.2 kWh per square metre a day. July is the sunniest month (93%) and December the cloudiest (56%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 59% | 1.4 |
| February | 65% | 2.3 |
| March | 68% | 3.5 |
| April | 74% | 5.2 |
| May | 77% | 6.2 |
| June | 82% | 7.1 |
| July | 93% | 7.7 |
| August | 91% | 6.5 |
| September | 86% | 4.8 |
| October | 76% | 3.0 |
| November | 64% | 1.6 |
| December | 56% | 1.1 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Hermiston need?
A normal year in Hermiston brings 4,859 heating degree days, 10% fewer than the median U.S. place (5,373), and 841 cooling degree days, 7% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,173 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 899 | 0 |
| February | 720 | 0 |
| March | 577 | 0 |
| April | 369 | 2 |
| May | 155 | 39 |
| June | 38 | 116 |
| July | 3 | 333 |
| August | 6 | 281 |
| September | 81 | 68 |
| October | 383 | 3 |
| November | 705 | 0 |
| December | 925 | 0 |
| Year (annual) | 4,859 | 841 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00004113. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Hermiston been warmer than normal lately?
2024 averaged 54.6°F, 0.7°F above the 1991-2020 normal of 53.9°F. 2 of the 3 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 55.7°F | +1.8°F | 6.67 |
| 2022 | 53.3°F | −0.6°F | 11.55 |
| 2024 | 54.6°F | +0.7°F | 11.02 |
Source: observed years: ACIS, station USW00004113. A year counts only with all twelve months complete.
How does Hermiston's climate compare?
Hermiston is warmer than 83 of the other 104 places with their own NOAA record in Oregon, and wetter than 2. Across the 7,247 U.S. stations with normals, its annual mean of 53.9°F is warmer than 57%.
In the Köppen classification computed from these normals, Hermiston is BSk: cold semi-arid steppe. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
What do Hermiston's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Hermiston. This page uses Hermiston Municipal Airport; the other differs by site and elevation:
| Station | From the center | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Hermiston (2 mi NW) USC00353818 | 2 mi NW | 460 ft | 52.0°F | 26°F | 89°F | 8.8 | – | April 27 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Hermiston's climate
What is the coldest month in Hermiston?
December, with a normal high of 42°F and a normal low of 28°F. The warmest is July (93°F by day, 59°F at night).
Does it snow in Hermiston?
Yes. NOAA publishes no 1991-2020 snowfall normal for Hermiston's NOAA station; the nearest record that keeps one, Boardman (21 miles away), records 4 inches of snow in a normal year.
What is the rainiest month in Hermiston?
January, with 1.14 in of precipitation in a normal year; the driest is July with 0.12 in.
What plant hardiness zone is Hermiston in?
The USDA's 2023 map puts Hermiston in zone 7b in ZIP code 97838, the nearest ZIP area. By the same method at Hermiston's NOAA station, the coldest night of a typical year reaches 2°F (22 years, 1991-2020): zone 7a.
How late can frost come in Hermiston?
In half of years the last 32°F night comes after April 26; in one year in ten it comes after May 10. Waiting until May 10 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Oregon climateThe statewide normals and every place in the state
- McNary Dam #2, OR7 miles from this station, 53.9°F a year
- McNary Dam, WA8 miles from this station, 54.2°F a year
- Boardman, OR21 miles from this station, 54.0°F a year
- Pendleton, OR22 miles from this station, 52.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made